Substituent rearrangement and elimination during noncatalyzed Fischer indole synthesis

Abstract

Treatment of 2,3,3-trimethyl-4-pentenal phenylhydrazone in refluxing ethylene glycol led to l-(3-methylbut-2en-1-yl) -3-methylindole, presumably through allylic rearrangement to the indolic nitrogen of the intermediate 3-(1,1 -dimethylallyl) -3-methylindolenine; no rearrangement to a 4-allylindole derivative was observed. Treatment of l,3-cyclohexanedione-2-chloro-6-(3-methylbut-2-en-l-yl) phenylhydrazone in refluxing o-dichlorobenzene led to 5-allyl-7-chloro indole derivatives, while in aqueous sulfuric acid a 4-alkyl-7-chloro indole derivative was obtained. These derivatives presumably arise via rearrangement of a C-3a isoprenylated intermediate. The formation of these products is discussed in relation to ergot alkaloid biosynthesis.

Selenonium Ylides: Syntheses, Structural Aspects, and Synthetic Applications

“…Reich and Cohen reported that the seleno-substituted ketone enolates can undergo an alkylation at the heteroatom [76]. Treatment of the appropriate enolate of α-(phenylseleno)acetophenone 154a with prenyl iodide or bromide led to the alkylation product 155a and unexpected product 156a (Scheme 40).…”

“…To confirm the ylide mechanism, the alkylation of α-allylselenoacetophenone 159 was performed. One of the reaction products was C-allyl product 160, which must be formed by the [2,3]-sigmatropic rearrangement of the intermediate 161 capable of allyl migration [76] (Scheme 41). To confirm the ylide mechanism, the alkylation of α-allylselenoacetophenone 159 was performed.…”